Method of and apparatus for hot-dip coating strands



3,082,119 METHOD oF AND APPARATUS FOR HOT-DIP coA'rING STRANDS FiledFeb. 24, 1960 *March 19, 1963 A. w. HARRIS 2 Sheets-.Sheet 1 March 19,1963 A. w. HARRIS 3,082,119

METHOD OF' AND APPARATUS FOR HOT-DIP COATING STRANDS Filed Feb. 24, 19602 Sheets-Sheet 2 A fior/rey Filed Feb. 24, 19.60, Ser. No. 10,639 .6Claims. (Cl. 117-114) This invention relates to an i-mproved method andapparat-us for hot-dip coating a continuous lmetallic strand with ametal or `alloy having a substantially lower melting point than themetal or alloy of the strand and more particularly to an improved methodfor the continuous hot-dip coating ofV a steel strand with a moltenmetal, such as aluminum, which does. not readily wet steel.

Conventional processes of hot-dip coating are of two general varieties.The first is characterized Iby passing .the cleaned base metal through aux and then into a molten bath of the coating metal. InV the second, thecleaned metal is heated in a reducing atmosphere and passed into themolten coating metal while still under the protection ofthe atmosphere.The aim in both instances is to bring clean metallic surfaces intocontact and thus achieve a complete wetting of the base metal with themolten coating metal. Complete wetting is essential .to .avoidblack-spots, (uncoated areas). It is Well recognized that the use of ux,either liquid or gaseous, for -this purpose presents severaldisadvantages. Moreover, this critical objective is not attained byeither `c`:onventional procedure when applied in the coating of ,acontinuously moving strand except at rather low rates of strandmovement. In the case of aluminum .coated ,steel wire, black-spots arenot completely eliminated even at impractically low strand speeds.

Accordingly it is an ,object of the present invention to provide animproved continu-ous hot-dip coating process wherein smooth coatingsfree .of even minute uncoated areas-can .be produced at highspeedwithout use of fluxes or preheating in a reducing atmosphere.

Another disadvantage of prior art practices has been the inability toproduce a perfectly valuminum coated `strand having .high tensilestrength. This derives from the fact that the coating bath must tbemaintained ata temperatureof 1100 to `1300 F. dependingupon the purityVof aluminum used and the steel brought to this temperature by fthe bathitself or by preheating. Thus in conventional practices `:because of therelatively slow rates of strand travel, the steel is substantiallyannealed, and the ,desired effects of prior cold Working or heattreatment to raise tensile properties of the steel are largely lost.Similar diiliculties, .but to a somewhat lesser degree are encounteredin `continuous hot -galvanizing and tinning operations.

Accordingly another object of the invention is the provision of hot-dipcoating process in which time at coating temperature is so short thatphysical properties of .the base metal are not substantially reducedthereby; a .particular object being production of hot-dipaluminum coatedsteel strands having tensile strength in excess 4of 2001,000i,p.s.i.

Another problem encountered in adapting conventional 4procedures ofhot-dip aluminum coating of steel strands has been .the cont-rol ofthickness of the alloy Vlayer -produced ,during the passage ofthe strandthrough the molten 4coating bath. The development of some intermetallic.compounds between the base and coating metals is 'beneficial,increasing adherence, improving soldering charac- `teristics and thelike. Excessive alloy however is detrimental, consequently controlofalloy formation has been the subject `of intensive investigation.Since maximum speed of travel in conventional hot-dip procedures is Xedarent O "ice by `other considerations, 'the conventional solution toalloy control has been to alloy the coating bathwith a metal which tendsto suppress alloy formation. While such practices have been successfulto a considerable degree, they introduce certain undesirablelimitations, for example, the use o f a feW percent of silicon in thealuminum bath reduces the alloy formation but at the same time adverselyaffects other characteristics of the coating itself.

Accordi-1q1gly, it 4is a further object of 4the invention to provide ,animproved Vprocess which permits the use of unalloyed coating baths.

Other objects will appear vas the description proceeds.

Heretofore control of black-spots to even `a reasonable Vdegree inthehot-dip aluminum coating of steel has required limi-,ting strand speedv.to a maximum of about 4G feet per minute; the maximum varying somewhatwith Athe dimensions of the str-and beingcoated. Even at such Aslowspeeds vsome `black-spots or holidays are caused by gas evolution fromthe steel base through the molter coating -just before or just afteremergence from the c-oating bath.. l have found this speed limitation isremoved and black-spots and the like, completely eliminated b3`imparting, inV combination with certain other practicef .hereafter.,described, vibratory forces of a particular nature tothe strand as itenters the aluminum bath. Moreover, 1 have found that these practicesmake an unexpectedly large reduction in the time o f immersion anc' thatthe strand leaving the coating bath not only `carries la completeIcoating but little or no alloy is formed thereor during its passage`through the .-bath.

I am aware that the use of vibration to promote wettability in solderingoperations and the like has been proposed. However, such earlierproposals have in general been concerned with ultrasonic vibrations and`have never been successfully applied in the continuous coatingoperations outlined above. I have found that success in the `latteroperations requires strict adherence to the following principles:

Firstly, the vibratory forcemust be applied in such manner as to developa transient, random vibration in the strand, such being characterized byinnumerable frequen cies inexcess ofASO: cycles per second and anoverall ac .celeration in excess of 2.0 g. Secondly, the vibratory forcV .must-be appliedtothe `strand as near its entry into the po as -ispractical; the vibrations or vibratory energy imparte( tothestrandmustbe substantially dissipated or dampener .out-before the stra-nd isdischarged from the coating po 4into-the atmosphere and the strand mustbe moved at sub stantially no tension. The foregoing conditions are es.sentialto .avoiding `the development of standing waves ir `.the.exiting strand` which cause rough, uneven coating and even extensiveuncoated areas.

The lterm substantially no tension as used herein i understood to meannot-substantially more tension lthai is required to move the strandthrough the apparatus anc excludes the application of appreciable backtension.

The required transient, random type Vof vibrations an produced in thestrand by ,applying shock impulses a ,regular intervals whilerestraining movement of the strani in the direction of the blow. The aimis to produce 1 ,slight random movement of the strand `rather than movementof apar-ticular amplitude in aparticular plane. Ac Ycordingly,results are not associated with development i1 `the strand of motionhaving a particular frequency am level-of acceleration but rather withthe development o an extremelycomplex motion in which substantially al`frequencies over fa -relatively wide range falling withii the audiblefrequency band are present at about the sam` ,levellofacceleration Ihave not, for example, been abL Ato produce coatings at high speeds`completely free o black-spots by inducing a pure sinusoidal vibrationin th| strand. A minimum of 40 to 60` shock impulses pe4 encountered;the optimum rate within this range depending on the mass of strand, thedegree with which movement of the strand in the direction of impact islimited, and to some extent on lthe design of the vibrator itself. Thelowest frequency developing in the strand should be of the order of 80c.p.s. but may be as high as about 400 c.p.s. without adverse effect.Absence of frequencies below about 300 c.p.s. requires higher overallaccelerations which while not detrimental is wasteful of vibratingpower. The highest frequency developing in ythe strand may be in excessof 16,000 c.p.s. however the absence of frequencies over about 3000c.p.s. is not detrimental. The intensity of the induced vibrations isimportant and is conveniently defined in terms of acceleration asmultiples of g, the acceleration of gravity, 32.172. ft./sec./sec. InIthis regard, the value of acceleration associated with the full rangeof frequencies present in the motion, i.e., the overall acceleration, isthe determining factor. The required motion being both transient andrandom, the acceleration associated with any particular component(frequency) thereof may vary considerably from moment to moment; theoverall acceleration however, remains relatively constant and must bemaintained at at least 20 g for satisfactory coating results. Overallaccelerations as high as 5000 g have produced good results, but I preferto use the lowest acceleration commensurate with good results since moreeicient use of vibrating power with least wear of the vibrator isachieved. The important point in this regard is that the vibrations andvibratory energy imparted to the strand must be substantially above thatwhich would be absorbed or dissipated by the passage of the strandthrough the coating bath. A minimum acceleration of 20 g achieves thisresult. Optimum value of acceleration varies with the material, temper,shape and dimensions of the strand, the design of the imparting vibratorand its associated motion limiting device and thus must be determinedexperimentally for each installation. The presence of discrete peaks inthe frequency-acceleration curve are not detrimental, although extremelyhigh level peaks toward the lower end of the frequency range may, undersome conditions, contribute to the formation of standing waves in theexciting strand, which condition must be avoided if smooth, black-spotfree coatings are to be produced.

Control of motion in the strand is conveniently accomplished byregulating the rate of application of the shock impulses. Other factorsbeing equal, the range of frequencies developing in the strand can beshifted upwardly and, more importantly, the overall accelerationassociated therewith can be increased by increasing the impact rate. Thefrequency range and acceleration can also be altered by increasing therestriction of strand movement in the direction of impulse application.Restricting strand movement increases the energy imparted per blow andcontributes to randomness of the motion achieved, for example, using animpact rate of 300 impulses per second against a restricted No. l gagelow carbon steel wire moving at 75 f.p.m. induced vibrations having anoverall acceleration of 1000 g and produced an excellent aluminumcoating; removing the restriction however altered the characteristics ofthe motion in the wire sufiiciently to adversely affect the coating andrequired increasing the impact rate to 900 impulses per second torestore coating quality. Accordingly, it is preferable in practicing myinvention to use a fixed degree of restriction at the imparting vibratorand adjust the impact rate if required.

Characteristics of the vibratory motion required in the present methodwere determined using an Endevco accelerometer and amplifier, a taperecorder, and a Bruel & Kiaer frequency analyzer and graphic levelrecorder.

A tape recording of the amplified output voltage of the accelerometerwas made while the vibration pick-up of the instrument was held manuallyagainst the vibrating strand. A loop of the tape was then played backcontinuously on the tape recorder and the electrical voltage producedwas -fed through the analyzer into the graphic level recorder to producea graph of vibration level as a function of frequency. The overallacceleration was computed from the graphed data.

In addition to greatly promoting wettability, induced vibratory motionsof the character described, greatly increases the rate of heat transferfrom the coating bath to the strand. The magnitude of the latter effectis such that time of immersion in the bath must be limited to a maximumof about 8 seconds if the benefits of the invention are to be obtained.Immersion time is a function of length of immersion and speed of strandtravel through the bath and is fixed in design of the coating pot andrigging. A minimum immersion of about 0.5 second must be provided toproduce satisfactory coating. Where minimum alteration of physicalproperties of the base metal is required, the immersion time should beas short as possible and preferably not more than about 3 seconds. Themaximum in -this regard varies somewhat with mass of the strand and bathtemperature.

A preferred arrangement of processing steps and apparatus suitable forthe practices of my invention is shown in the attached drawing, inwhich:

FIGURE 1 is a schematic side elevation, partly in section of a coatingline embodying the principles of my invention; t

FIGURE 2 is an enlarged longitudinal section of the coating pot ofFIGURE l;

FIGURE 3 is a partial end elevation of the coating pot;

FIGURE 4 is a plan of the vibration imparting mechanism;

FIGURE 5 is a sectional view taken along plane IV IV of FIGURE 4;

FIGURE 6 is a side elevation of the hold-down mechanism;

FIGURES 7 and 8 are respectively, a front elevation and a plan View of agas Wipe particularly adapted to the practices of my invention; and

FIGURE 9 is a sectional View thereof taken along the plane IX-IX ofFIGURE 8.

With particular reference to the drawing, the numeral 2 designates acoil of strand or wire S disposed on a pay-off reel 4 which is powerdriven and provided with conventional controls, not shown, forautomatically regulating the speed thereof. Located at the other end ofthe line is a power-driven take-up reel or recoiler 40 also providedwith conventional controls, not shown, for automatic speed regulation.Reels 4 and 40 are operated to feed and gather strand S at the samelineal rate so that the strand will be moved through the apparatus atsubstantially no tension. From the pay-olf reel, the strand S may be fedthrough cleaning tank 6, preferably a tank of molten caustic and thenthrough a water rinse 8. Alternately or sequentially the strand may beconducted through a tank 10 containing a dilute aqueous sulphuric orhydrochloric cleaning solution followed by a water rinse 12. Cleaningarrangement shown is particularly adapted to the removal of thelubricants and .drawing compounds conventionally used in the colddrawing of wire. The molten caustic breaks down the drawing lubricantsto a readily removable form and complete neutralization and cleansing iseffected by the acid bath. Methods better adapted to other materialscan, of course, be substituted. Preferably the strand is next conductedthrough a hot Water rinse tank 14 to further rinse the strand, expel asmuch adsorbed gas as possible, and promote drying thereof. Drying issubstantially completed by a hot-air or similar drier 16, after whichthe strand is passed into contact with a rotary impact-impartingmechanism V for inducing vibratory motion of the required character inthe strand. An adjustable, resiliently mounted hold-down sheave 18located just ahead of the mechanism V maintains the strand in suitablecontact therewith to restrict strand movement in the direction `ofapplication of impact; the yamount of such restriction being regulatableby adjustment of spring pressure on the sheave. From vibrator V thestrandpasses through an elongated tube22 havingone end submerged in abath 20 of molten coating metal. A gas inlet 24 is provided adjacent thelower end of the tube and a nonoxidiz'ing or reducing gas iscontinuously introduced to maintain a nonoxidizing atmosphere in contactwith the bath-surface at the point of entry of the strand. If the gas iscombustible, it may be burned at the `upper end of .the tube as it exitstherefrom. Vibrator-y motion induced in strand S rapidly dissipates anyabsorbed gas or Water films from the `strand and 'disrupts any oxide`films formed on the bath surface, however, exceptionally heavy topdross is produced; accordingly, the steps `for vdrying the strand and.maintaining the bath surface free of oxide while not essential tin thepresent methodto the production of a quality aluminum coating, areincluded lfor economic reasons. The flow of gas through tube 22 carriesaway the gases and any water vapor evolved from the strand by the`imparted vibration and maintains the surface `of the coating metal ratthe point of strand entry -completely free of oxide, accomplishing thisobjective without lthe formation of any deleterious side reactionproducts. In coating withzinc or tin, drying of the strand is, ofcourse, a `necessary 'safety measure. The strand is submerged inthecoating metal by `a sinker 26, passing therefrom in a substantiallyvertical pass-line to a de- Viiector rol-l 34 located a suicientdistance above the bath to -avoid contacting the strand -prior -tocomplete solidification of the coating thereon. ranged to direct a blastof -cool air or atomized Water against the strand to arrest alloyformation, may be positioned below sheave 34. Means 35 should besupported in an ladjustable manner to `bepositionable in the pass as maybe required. The coated strand leaves the bath through a speciallyconstructed gas wipe 30, lpartially submerged in `the molten coatingmetal. Wipe 30, shown yin detail in FIGURES 7, 8, and 9, comprises anopen-bottom, box-like chamber A having in the top thereof, an opening431 for the passage of the coated strand and a gas inlet 32. Acombustible gas, e.g. natural gas, Ais introduced at inlet 32 and burnedVat opening 31. The latter should be restricted to `a `size permitting afree dow of the gas completely around `the exiting strand but preventing4back-flow of air into -the chamber. The -burning gas promotes flow-backof excess `coating metaland maintains `the bath surface yfree of oxidesYand dross at the 'point-of strand -exit toinsure bright, uniformcoatings. Extending the width of .chamber 30A several linches above thebottom thereof and disposed below opening 31"soas to contact-a strand:exiting therethrough Vis a rod '-28 of Alundum or like materialsupported at one end by the blind recess in boss 127A- and` by `thethreaded opening in-boss 327B at `the other, threaded plug `27C serving4to -clamp the rod iin thisposition. Rod ZS is :preferably grooved 4totprevent strand S from rubbing the side walls .of opening 311.Projecting from 4one side of chamber 39A and aligned to permitobservation of the contact .of strandSand .bar 28 isa sight tube 29, theend of which is .closed to the latmosphere by a suitable sgiass disc29Aanddclamping ring 29B. Support ar-m 30B weld-ed .or .otherwiseattached to the back-of chamber 39A, :is slidably disposed in a `clamprwhich lin turn isr-slidably attached .to vertical standards 25carriedby the bac-k `wallZA of the coating pot.

As previously mentioned, the .present invention .contemplates prevention`of standing waves in the strand leaving the coating .pot by maintaining`the strand substantially untensioned and dissipatingza substantialportion of the energy limparted by vibrator V before discharging theAcoated strand into the atmosphere. The

Cooling means ar- I latter is accomplished by `positioning, wipe 30 sothat bar 28 bears against strand S at a point ll/z to.3 inches above-the surface of the molten .coating metal to deflect the strand from thepositionit would, by reason of its substantially untensioned condition,otherwise normally assume in passing lfrom sinker 26 to sheave 34. Thedegree of deflection must be such as will develop sufficient pressure tomaintain a positive contact of strand and bar at all times, butinsuicient to remove the coating at the point of contact.

Since for any given deflection, the pressure of contact depends upon theresilience of the strand which in turn varies with such factors -asstrand composition, its crosssectional dimensions and prior treatmentsVaffecting its mechanical properties, the position of wipe 30 must beadjusted for diiferent strands. Itis impossible to assign numericallimits of either deflection or pressure, accordingly, necessaryadjustments must be made by Observaion of results.

Location of contact bar 28 is of `critical importance tc the practicalachievement of the results of my invention Complete submersion favorsdissipation of the vibratory energy from the strand and does so Withoutdamage tc 4the coating. A completely submerged bar, however, :be haveserratically; such ibars frequently disintegrate in exceedingly shorttimes. Moreover, adjustment of a sub merged bar is very diiiicult andtime consuming. On the other hand, rough, oxidized streaks and othercoating defects resulting from contacting the molten coating can not betolerated. I have found the foregoing diflicultie: are completelyavoided and the required dissipation o: vibra-tory energy achieved onlyif the contact is mad within the gas Wipe a few inches above the bathsurface Due to the upward drag of molten metal by the rapidly movingstrand, the coating at this location lis abnormally thick, is fullymolten and is protected against` oxidatior by the atmosphere of thewipe. Under these condition: the disturbance of the coating lby thesqueegeeing actioi of the contact bar has no permanent elfect and thecoat ing produced is uniform and free of oxide streaks. Fo: effectivedampening, however, contact must be made with in l-/z and 3 inches ofthe bath surface, depending some what on the speed of travel, size, :andmechanical prop erties of the strand. The bar is easily adjusted sinclcontact-can be observed through the sight tube Z9;

From sheave 34 the'coated strand may be conveyed bj suitable arrangementof rolls or sheaves, through con ventional means indicated at 36 and 38to further cool treat, or ylubricate the product as desired. Thereafte'the strand is wound on talre-up reel 40 previously de scribed. Since itis essential to the purposes of my in `vention that the strand does notybecome taut during it passage through the equipment, care must be takenin de sign -to minimize friction at, as well as the number oi `conveyingrolls or sheaves. Straightthrough-type 4treat ing tanks should be usedwherever possible.

A preferred embodiment of the vibrator V is shown i1 FIGUR-ES 4 and 5 ofthe drawing. lt is` comprised of variable speed motor A50 connected to apair of oppose discs v52. Disposed `between the discs are la plurality oequally spaced pins or bars 54 spaced inwardly a sligh distance fromIthe periphery of the :discs as shown i1 FIGURE 5. The assembly issupported on va plate 5i from the'forward wall of `coating-pot 2A)`withwthetop edge of the discs 52 projecting above lthe normal pass lineo the strand. Thus, the str-and rides loosely between th discs and issubjected ytofan impact by each pin as th discs rotate. Hold-down sheavev18 positioned to'rideeth surface of the strand a `slightfdistance aheadof disc 52 is carriedyby a bearing bracket 58 which is tit-ted t slidey'freely on a pair -of supportrods `60. A spring 6.' is positionedbet-Ween the bracket 58Hand a retainer ba 64; the latter being`adjustafbly secured to supports Y6 Thus, sheave 18 resiliently -urgesthe strand -into contac with the pins and resiliently restricts themovement o the strand in the direction of the impacts applied by thepins. Spring pressure determines the amount of restriction and isregulatable by adjusting the position of the retainer bar `64. Lateraldisplacement of the strand by the impacts is prevented by the projectingedges of discs 52. Conventional means (not shown), for controlling -thespeed of the motor S` are provided so that the impact rate may beregulated. Direction of rotation of motor 50 is selected to drive discs52 in the direction of strand travel to aid strand movement through thecoating bath and thus minimize tension build-up. Thus, the describedarrangement is particularly suited to the purposes of the presentinvention.

The following specific examples serve to illustrate the practices andresults of the invention.

Example A Cold drawn, high-carbon steel wire, size 0.103, grade SAEC-1085 having a tensile strength in excess of 200,000 p.s.i., washot-dip coated with aluminum containing 3% silicon at a speed of 130fpm. to provide a defect free coating without affecting the tensileproper-ties of the steel by the -following sequence of treatment:

The wire was continuously fed from a pay-off reel 4 and passedsuccessively through molten sodium hydroxide, maintained at between 800and 950 F. in tank 6, Water rinse 8, a cold dilute muriatic acid bath yand a cold water rinse 12 to remove the drawing lubricant and anyforeign material from the surface thereof. The cleaned wire was dried bypassing it through hot water tank 14 and hot-air drier 16'. Hold-downsheave 18 was adjusted to provide a medium level of resilientrestriction and the vibrator V, which consisted of ten 10) Vs" diameterpins 54, equally spaced about a 5%" diameter circle on discs 52, wasrotated to impart 360 impacts per second to the wire. These particularconditions induced vibrations in the wire having frequenciescontinuously distributed over the frequency range 80 to 10,000 c.p.s. atan overall acceleration of 1200 g. The wire was introduced into thecoating pot through tube 22 in which a small flow of natural gas wasmaintained through inlet 24, the gas being allowed to burn at the upperend of the tube. The bath was maintained at about 1200 F. and the lengthof wire immersion therein was about 4 feet, thus, provided an immersiontime, at 130 f.p.rn., of 1.85 seconds. After passing around sinker 2.6the wire left the bath through gas wipe 30 wherein a small flow ofnatural gas was maintained through inlet 32 and allowed to burn aroundthe strand at the opening 31. With the strand moving at speed (130 fpm.)the position of wipe 30 was adjusted to bring bar Z8 into a uniform andpositive contact with the Wire at a point about 11/2 inches above thebaths surface with a pressure just short of -tha-t which will cause -adry-streak or other damage in the coating. The wire was -allowed to coolnaturally to the solidication temperature of the coating in its upwardpassage to sheave 34. Temperature of the Wire was further reduced bypassing through Warm water in tank 36', a film of oil `applied in tank3S and the coated wire recoiled by take- -up reel 40. A clear, brightaluminum coating amounting to 0.36 oz. per square foot of wire surfacewas 0btained. The coating was completely free of black-spots and couldbe formed into the standard wire Ibut-ton test without cracking orpeeling. The alloy layer formed was uniform and slightly less thannormal. Tensile tests of the wire showed substantially no change in thephysical properties of the base metal.

Example B Materials and conditions were the same as in Example A exceptthat the use of the hot water rinse 14, the drier 16 and the bath entrytube ZZ was eliminated. insofar as product was concerned, results werethe same as in A but, a large amount of top dross was produced at theentry end of the coating pot. While the dross did not interfere withcoating, it represents a substantial loss of coating metal.

Example C Cold drawn wire, size 0.103, grade SAE C-1060 was coated usingthe same sequence as Example B except that acid cleaning 10 Was alsoeliminated, the vibrator was operated to impart 450 impacts per secondand the speed of the line reduced to f.p.m. At this speed a coating of0.295 oz. per square foot was produced. Overall acceleration of motionin the wire was 1000 g, immersion time in bath was 2.4 seconds. Coatingwas bright and completely free of black-spots, although the wireentering the coating pot carried a visible brown film.

Example D The wire of Example C was coated using an impact rate of 175impacts per second at a speed of 136 f.p.m. The overall acceleration ofthe vibratory motion imparted was about 400 g and immersion time in thebath was about 1.75 seconds. Again, clear, bright, black-spot freecoatings of unsually high adherence were achieved.

Example E Low carbon steel wire, size 0.0625, was coated using thesequences utilized in Example A. In this instance a vibrator consistingof sixteen (16) diameter pins equally spaced about a 5% diameter circleon discs 52 was rotated to impart about 600 impacts per second and theline operated at f.p.m. Hold-down sheave 18 was adjusted to providelight pressure and three levels of overall acceleration (25, 60 and 100g) in the motion induced in the Wire. Time in the coating bath was 2.0seconds. In all instances bright, clear, black-spot free coatings wereproduced.

Example F Low carbon steel wire, size 0.135 inch was coated using thesequence outlined in Example A at 75 f.p.m. using a vibrator consistingof twelve (12) 1%" diameter -pins equally spaced about a 5% circle ondiscs 52. Hold-down sheave 18 was adjusted to apply a medium restrictivepressure. The vibrator was rotated to apply impact rates varied 200 to800 per second, inducing random trransient motion in the wire at levelsvarying from 2000 to 2750 g. Immersion time was 3.2 seconds. Exceptionalcoatings were obtained over the entire range.

-In general wires as small as 0.04" in diameter and as large as 0.238"have been coated successfully and all advantages of the present methodachieved. Aluminum coatings amounting to 0.50 oz. per square foot havebeen applied to 0.080 size wire at 200 fpm.; also to 0.148 size wire atand 220 f.p.m. In the case of large diameter wire, it has provenadvantageous to use a rotating sinker and remove the wire from the bathat an angle rather than in a vertical pass; this reduces dragging at thesinker and aids in avoiding deleterious standing waves in the exit pass.

Speeds up to 250 f.p.m. (about six times the maximum speed possibleheretofore), have been used. Operations at high speed permit reductionof the immersion time to less than 1 second. The latter, coupled withthe fact that vibrating in the manner described greatly increases therate of heat transfer, affords a degree of control of alloy formationnot heretofore available. This may be illustrated by the fact that thecoated wire of Example A can be produced substantially free of alloylayer by quenching the coated strand as it emerges through the gas wireby passing it through the cooling device 35 wherein it is sprayed withsteam, atomized water or s1mply with a blast of cold air. This result isobtained even with a bath of substantially pure aluminum maintamed at atemperature of about 1235 F. By regulating the position of cooler 35 inrelation to the speed of travel of the strand, the optimum amount ofalloy layer consistent with good adhesion, brightness of coating andother desired characteristics can be produced.

As used in the foregoing description, the term strand includes singleVcontinuous lengths of metallic strip "or wire as well as a pluralityVof lengths twisted or otherwise grouped together.

This application is a continuation-in-part of my copending applicationSerial No. 743,616, led June 23, 1958, now abandoned.

While the foregoing examples have illustrated application of myinvention to the aluminum coating of steel, it is not limited theretobut can be applied with advantage in the continuous hot-dip galvanizingand tinning of steel and other basis metals.

I claim:

1. A method of producing cold drawn aluminum coated steel wire having ahigh tensile strength characterized by freedom from black spots fromcleaned, cold drawn wire comprising continuously advancing the cleanedwire in a substantially untensioned condition through a fluxyfree bathconsisting essentially of molten aluminum at -a speed in excess of 40fee-t perminute and with an immersion time of not more than about 3seconds, applying at least 40 shock type impulses per second to the wireadjacent the entry portion of the bath while restricting movement of thewire in the direction of application of the shock type impulses adjacentthe point of application thereof to produce transient random vibrationsin the strand characterized by the presence of innumerable frequenciesin excess of about 80 c.p.s. and an overall acceleration value in excessof 20 g whereby the surface o-f the lwire is continuously wetted to forman uninterrupted molten sleeve `of coating metal thereon, saidvibrations having sufcient intensity to dislodge the coating metal fromthe wire as it emerges from the bath if not dampened, the shock typeimpulses being applied to the wire in the direction of travel thereof tomaintain the wire in said substantially untensioned condition,positively dampening the vibration of said substantially untensionedcoated wire before it contacts the air to prevent the molten coatingmetal being dislodged therefrom, withdrawing said wire from the bath inan upward directionand quickly quenching the molten coating metal tominimize the alloy layer formation before changing the direction ofmovement of the coated wire.

2. A method of producing cold drawn aluminum coated steel wire having atensile strength in excess of 200,000 p.s.i. characterized by freedomfrom black spots comprising cleaning the cold drawn wire to remove thecold drawing lubricants therefrom, continuously advancing the cleanedwire in a substantially untensioned condition 4through a flux-free bathconsisting essentially of molten aluminum with an immersion time of notmore than about 3 seconds, applying at least 40 shock type impulses persecond to the wire adjacent the entry portion of the bath whileresiliently restricting movement of Ithe strand in the direction ofapplication of the shock type impulses adjacent the point of applicationthereof to produce transient random vibrations in the strandcharacterized by the presence of innumerable frequencies in the range ofabout 80 to 10,000 c.p.s. and an overall acceleration value in the rangeof 100 to 1000 g whereby the surface of the wire is continuously wettedto form an uninterrupted molten sleeve of coating metal thereon, saidvibrations having sufficient intens-ity to dislodge the coating metalfrom the wire as it emerges from the bath if not dampened, withdrawingsaid substantially untensioned wire from the bath in a verticaldirection through a nonoxidizing atmosphere, positively dampening thevibration of said wire suiciently as it leaves the ba-th and While insaid nonoxidizing atmosphere to prevent the molten coating metal beingdislodged therefrom and continuing the vertical travel of the wire for asufficient d-istance to permit the molten metal to freeze with a smoothsurface before changing the direction of movement of the coated wire.

3,. A method of producing aluminum coated steelwire having good physicalproperties Vcharacterized by freedom from black spots from cleaned, colddrawn steel wire comprising continuously advancing the cleaned Wire in asubstantiallyuntensioned condition through a substantially moltenaluminum flux-free coating bath at a speedin excess ofA 40feetperrninute and with an im- 'mersion time of not'more thanabout 8seconds, applying at least 40 shock type impulses per second to the wireadjacent the entry portion of the bath while restricting movement of thewire in the direction of application of the shock .type impulsesadjacent the point of application thereof to produce transient randomvibrations in the strand characterized by the presence of innumerablefrequencies in excess of about c.p.s. and an overall acceleration valuein excess of 20 g whereby the surface of the wire is continuously wettedto form an uninterrupted mol-ten sleeve of coating metal thereon, saidvibrations having sufficient intensity to dislodge the coating metalfrom the wire as it emerges from the bath if not dampcned, positivelydampening the vibrations .of said substantially untensioned coated wirebefore it contacts the air to prevent the mol-ten coating metal frombeing dislodged therefrom, withdrawing said wire from the bath in anupward direction and continuing the upward travel of the wire forsuicient distance to permit .the coating metal to freeze with a smoothsurface before changing the direction of movement of the coated wire.

4. Apparatus for continuously hot-dip coating strand comprising meansfor continuously advancing strand through a bath of molten coatingmetal, vibrating means at the entry end of the bath for imparting atleast 40 shock type impulses per second to the strand and producerandom, transient vibrations in the strand traveling lthrough the moltencoating metal characterized by the presence of innumerable frequenciesin excess of about 80 c.p.s. and an overall acceleration value in excessof 20 g, positive vibration dissipating means at the exit end of thebath adapted to contact said strand prior to its discharge into the air,and means adjacent the vibrating means for resiliently restrictingmovement of the strand in the direction of application of the shock typeimpulses.

5. Apparatus for continuously hot-dip coating strand comprising meansfor continuously advancing strand through a bath of molten coatingmetal, rotary vibrating means at the entry end of the bath for impartingat least 40 shock type impulses per second to the strand and producerandom -transient vibrations in the strand traveling through the moltencoating metal characterized by the presence of innumerable frequenciesin excess oi abou-t 80 c.p.s. and an overall acceleration value inexcess of 20 g, positive vibration dissipating means at the exit end ofthe bath adapted to contact said strand prior to its discharge into theair, adjustable means for urging the strand into contact with thevibrating meansi and variable speed driving means for the vibratingmeans, said driving means being adapted to rotate the vibrating means sothat the impact is applied in the direc-tion ol movement of the strand.

6. Apparatus -for continuously hot-dip coating strane' comprising meansfor continuously advancing strand through a bath of molten coating metalin a substantially untensioned condition, rotary vibrating means a theentry end of the bath for imparting at least 40 shocl type impulses persecond to the strand and produce random transient vibrations in thestrand traveling througl the molten coating metal characterized by thepresence of innumerable frequencies in excess of about 80 c.p.s and anoverall acceleration value in excess of 20 g, posi tive vibrationdissipating means at the exit end of the bath adapted to contact saidstrand prior to its discharg into the air, and driving means. for therotary vibrating means, lsaid driving means being adapted to rotate therotary vibrating means so that the impact is applied in 2,731,362Brondyke Jan. 17, 1956 the direction of movement of the strand.2,895,845 `Jones et al July 21, 1959 2,900,273 Linden Aug. 18, 1959References Cited in the le of this patent 2,906,018 Baker Sept. 29, 1959UNITED STATES PATENTS 5 1,770,910 Byrd July 22, 1930 1,933,401 Ward Oct.31, 1933

1. A METHOD OF PRODUCING COLD DRAWN ALUMINIUM COATED STEEL WIRE HAVING AHIGH TENSILE STRENGTH CHARACTERIZED BY FREEDOM FROM BLACK SPOTS FROMCLEANED, COLD DRAWN WIRE COMPRISING CONTINUOUSLY ADVANCING THE CLEANEDWIRE IN A SUBSTANTIALLY UNTENSIONED CONDITION THROUGH A FLUXFREE BATHCONSISTING ESSENTIALLY OF MOLTEN ALUMINUM AT A SPEED IN EXCESS OF 40FEET PER MINUTE AND WITH AN IMMERSION TIME OF NOT MORE THAN ABOUT 3SECONDS, APPLYING AT LEAST 40 SHOCK TYPE IMPULSES PER SECOND TO THE WIREADJACENT THE ENTRY PORTION OF THE BATH WHILE RESTRICTING MOVEMENT OF THEWIRE IN THE DIRECTION OF APPLICATION OF THE SHOCK TYPE IMPULSES ADJACENTTHE POINT OF APPLICATION THEREOF TO PRODUCE TRANSIENT RANDOM VIBRATIONSIN THE STRAND CHARACTERIZED BY THE PRESENCE OF INUMERABLE FREQUENCIES INEXCESS OF ABOUT 80 C.P.S. AND AN OVERALL ACCELERATION VALUE IN EXCESS OF20 G WHEREBY THE SURFACE OF THE WIRE IS CONTINUOUSLY WETTED TO FORM ANUNINTERRUPTED MOLTEN SLEEVE OF COATING METAL THEREON, SAID VIBRATIONSHAVING SUFFICIENT INTENSITY TO DISLODGE THE COATING METAL FROM THE WIREAS IT EMERGES FROM THE BATH IF NOT DAMPENED, THE SHOCK TYPE IMPULSESBEING APPLIED TO THE WIRE IN THE DIRECTION OF TRAVEL THEREOF TO MAINTAINTHE WIRE IN SAID SUBSTANTIALLY UNTENSIONED CONDITION, POSITIVELYDAMPENING THE VIBRATION OF SAID SUBSTANTIALLY UNTENSIONED COATED WIREBEFORE IT CONTACTS THE AIR TO PREVENT THE MOLTEN COATING METAL BEINGDISLODGED THEREFROM, WITHDRAWING SAID WIRE FROM THE BATH IN AN UPWARDDIRECTION AND QUICKLY QUENCHING THE MOLTEN COATING METAL TO MINIMIZE THEALLOY LAYER FORMATION BEFORE CHANGING THE DIRECTION OF MOVEMENT OF THECOATED WIRE.